FACTION_PROP.INI

[FactionProps]
affiliation = li_n_grp
legality = lawful
nickname_plurality = singular
msg_id_prefix = gcs_refer_faction_li_n
jump_preference = jumpgate
npc_ship = li_n_li_elite_d1-3
npc_ship = li_n_li_elite_d4
npc_ship = li_n_li_elite_d5
npc_ship = li_n_li_elite_d6
npc_ship = li_n_li_elite_d7
npc_ship = li_n_li_elite_d8
npc_ship = li_n_li_elite_d9
npc_ship = li_n_li_elite_d10
npc_ship = li_n_li_elite_d11-19
npc_ship = li_n_cruiser_d22
npc_ship = li_n_dreadnought_d25
voice = pilot_f_mil_m01 <---------------
voice = pilot_f_mil_m02 <---------------
voice = pilot_f_leg_f01 <---------------
voice = pilot_f_leg_f01a <---------------

that handles the pilots in space. The bartender would be in mbases:

[GF_NPC]
nickname = li0101_fix_bartender
body = li_bartender_body
head = rh_bartender_head
lefthand = benchmark_male_hand_left
righthand = benchmark_male_hand_right
individual_name = 244609
affiliation = li_p_grp
voice = rvp101 <---------------------
(the other dealers have declared voices, but they were never completed, so ignore)

and the docking voice would be at each base:

[Object]
nickname = Dock_Ring_Li01_01
ids_name = 261168
pos = -33267, 0, -28810
Archetype = dock_ring
ids_info = 66141
dock_with = Li01_01_Base
voice = atc_leg_f01a <---------------------
space_costume = , robot_body_A
reputation = li_p_grp
behavior = NOTHING
difficulty_level = 1
loadout = docking_ring_li_01
pilot = pilot_solar_easiest

First look through the above and decide which voices you will limit the new faction to (so you don't have to make entries in all 50 some voices). If you use what I have above then there are 6 voices you need to edit.
You will need to either create a new sound clip to speak your new faction name or just use the one for li_n. Extract it from the utf files and reinsert it with the new name in all the files you need to. Then make the ini edits like you posted above. It is the only way to get rid of the errors and still have them speak.
You probably already know about my tutorial at FLC to do this.
There is another way to simply remove the error but they won't speak the new name then.

[FactionProps]
affiliation = fc_uk_grp
legality = unlawful
nickname_plurality = singular
msg_id_prefix = ignore <-------------------

That is a vanilla entry, I have no idea if it still throws an error, worth a try for the easy fix.